Use FQDN in downburst yaml.

As newer rhel's like to default to localdomain screwing with things
if its not set. Older cloud-init/distros appear to just ignore the
domain.

Signed-off-by: Sandon Van Ness <sandon@redhat.com>
Merge pull request #383 from ceph/wip-downburst-fqdn

Use FQDN in downburst yaml.